The invention relates to a blower nozzle for heating and cooling web-like materials.
Blower nozzles of this type are used, for example, for heating or cooling web-like materials, in particular in the production of plastic foil. In this case, the blower nozzle is arranged transversely, i.e. generally perpendicularly, to the take-off direction of the material web, and thus transversely to the web running direction, above and/or below the material web.
It is particularly important for the foil process that the outflow from the nozzles is even, since uneven heating of the plastic foil during processing can have negative effects on the thickness profile. This is because slightly warmer regions are stretched more and are thus thinner than relatively colder plastic foil regions, which then obtain a somewhat thicker foil cross section. Uneven heating or cooling of the foil also leads, however, to a deterioration in the flatness of the final product.
Even blowing is particularly crucial for the production of ultrathin films or foil whose thickness can be reduced down to about 0.4 .mu.m.
Various proposals have already been made to even out the outflow speed for heating or cooling continuous webs of material, in particular plastic foil webs. EP-A1-0 377 311 proposes a blower nozzle having two supply chambers which are seated next to one another, extend transversely to the take-off direction of the material web, are provided, in each case opposite one another, with a supply aperture for the hot gas of the hot air, and are closed at their respective, opposite end. The cross section of the respective supply chamber decreases in a web-shaped manner from the supply aperture to the opposite, closed end parallel, in the side view, to the take-off direction of the plastic foil web. A distribution chamber is then seated below the two supply chambers arranged next to one another, with the result that the opposite hot gas flowing in at the end side via the supply chambers can then pass via overflow apertures, arranged between the two supply chambers and the distribution chamber, essentially transversely to the plane of the material web into the distribution chamber and from there can emerge in a transverse direction transversely to the plastic foil web via outlet apertures situated at the bottom.
Since two supply chambers which are symmetrically opposite to the central longitudinal direction of the plastic foil web are thus provided, it is possible for an equal distribution of pressure to be obtained which, even if it is not even is nevertheless at least symmetrical with respect to the cross section of the plastic foil web (i.e. transversely to the take-off direction thereof), thus enabling the plastic foil web to be subjected to the blowing action of air or gas as evenly as possible over the entire width of the blower nozzle.
However, this requires an increased outlay since two supply ducts are provided, which have to be supplied with hot gas or cooling gas (generally air) in each case on opposite sides, i.e. on both sides of the material web being advanced, in each case via a separate supply aperture. However, this results in relatively poor accessibility to the blower nozzle in particular if it is installed in an oven.
An essentially two-part veneer web drier has been disclosed, for example, in DE 30 35 417 A1. The nozzle box includes a perforated plate which runs obliquely from bottom to top, is provided with holes and divides the nozzle box into a pressure space and a suction space, the suction space being connected to the intake side and the pressure space being connected via the delivery side to circulating fans. Even a veneer web drier of this type does not result in the desired, completely even distribution and/or even gas outlet speed of the supplied hot gas flow over the entire length of the nozzle box.
In the case of the blowing device which is disclosed in DE 37 04 910 C1 or DE 36 26 171 C1 and is intended for blowing a treatment medium onto a material web moving in the longitudinal direction, just one chamber is provided which is simultaneously used as the supply and distribution chamber. In order to be able to supply hot gas at the two opposite, end supply apertures from just one side of the material web, some of the hot gas is supplied via a separate supply duct to the opposite, end connection aperture of the distribution chamber, via the additional supply duct, and is conducted into the distribution chamber.
A corresponding principle for a nozzle box for a device for the heat treatment of webs of endless fabric, in particular textile webs, has been disclosed to this extent in DD 253 666 A1 too.
Suspension nozzles have been disclosed, for example, in US patents U.S. Pat. Nos. 5,156,312 and 5,395,029. The medium can emerge from a supply chamber via two lateral control chambers upward in the direction of the material web which is being guided past and is to be treated, it being possible for the individual, lateral control chambers to be opened or closed in such a manner that an air flow in the direction of the take-off direction of the material web to be treated, a flow direction in the opposite direction thereto, or a symmetrical flow direction can be produced to the extent that some of the gas flowing out is deflected in the take-off direction of the material web and in the opposite direction.
Finally, DE 38 15 211 C2 has disclosed the design of a suspension nozzle having a plurality of chambers, which nozzle, however, because of its design results in the web of endless fabric W coming to lie between the outlet nozzles in a cross-sectionally rippled manner. A suspension nozzle of this type in particular cannot be used in the production of plastic foil webs which is advanced via tenter hooks acting laterally on the plastic foil web and is optionally stretched in the longitudinal and/or transverse direction.